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Monthly Archives: November 2014

Adapted from a press release of the Max Planck Institute for Extraterrestrial Physics, November 24, 2014:

Astronomers at the Max Planck Institute for Extraterrestrial Physics recently presented new observations of the gas cloud G2 in the Galactic Centre, which was originally discovered in 2011. These data are in remarkably good agreement with an on-going tidal disruption. As a complete surprise came the discovery that the orbit of G2 matches that of another gas cloud detected a decade ago, suggesting that G2 might actually be part of a much more extensive gas streamer. This would also match some of the proposed scenarios that try to explain the presence of G2. One such model is that G2 is originating from the wind from a massive star.

The gas cloud G2 is on a highly eccentric orbit around the Galactic Center. Observations in 2013 have shown that part of the gas cloud is already past its closest approach to the black hole, at a distance of roughly 20 light hours (a bit more than 20 billion kilometres).

The new, deep infrared observations with the SINFONI instrument at the VLT track the ongoing tidal disruption of the gas cloud by the powerful gravitational field. While the shape and path of the gas cloud agrees well with predictions from the models, so far there has been no significant enhanced high-energy emission, as one might have expected from the associated shock front.

Copyright and credit: Max Planck Institute for Extraterrestrial Physics

Copyright and credit: Max Planck Institute for Extraterrestrial Physics

However, a closer look into the data set led to a surprise. A decade ago, another gas cloud – now call G1 – was observed in the central region of our galaxy and it has a similar orbit. The researchers postulate that G1 and G2 might be clumps of the same gas streamer. G1 and G2 could be clumps in the wind ejected from of one of the massive disk stars in the vicinity. This could help to explain the missing X-ray emission from the gas cloud near the black hole (although the non-detection of such emission is not yet understood).

Links: MPE press release, including figures and detailed captions.

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From a JPL press release dated November 21, 2014:

Scientists have produced a new version of what is perhaps NASA’s best view of Jupiter’s ice-covered moon, Europa. The mosaic of color images was obtained in the late 1990s by NASA’s Galileo spacecraft. This is the first time that NASA is publishing a version of the scene produced using modern image processing techniques.

Credit: NASA/JPL-Caltech/SETI Institute

Credit: NASA/JPL-Caltech/SETI Institute

The new image more closely approximates what the human eye would see than the earlier version (released in 2001). The image features many long, curving and linear fractures in the moon’s bright ice shell. Scientists are eager to learn if the reddish-brown fractures, and other markings spattered across the surface, contain clues about the geological history of Europa and the chemistry of the global ocean that is thought to exist beneath the ice.

In addition to the newly processed image, a new video details why this likely ocean world is a high priority for future exploration.

Links: more details about the image above; Europa exploration movie; NASA’s Europa homepage.

Adapted from a UCLA press release, November 3, 2014.

For years, astronomers have been puzzled by a bizarre object in the center of the Milky Way that was believed to be a hydrogen gas cloud headed toward our galaxy’s enormous black hole. (See Section 15.5, Chapter opener figure, p. 382, and Figure 15-5, p. 388.)

Having studied it during its closest approach to the black hole this summer, UCLA astronomers believe that they have solved the riddle of the object widely known as G2.

A team led by Andrea Ghez determined that G2 is most likely a pair of binary stars that had been orbiting the black hole in tandem and merged together into an extremely large star, cloaked in gas and dust – its movements choreographed by the black hole’s powerful gravitational field. The research is published today in the journal Astrophysical Journal Letters.

Astronomers had figured that if G2 had been a hydrogen cloud, it could have been torn apart by the black hole, and that the resulting celestial fireworks would have dramatically changed the state of the black hole. However, G2 survived and continues on its orbit unaffected.

G2 appears to be just one of an emerging class of stars near the black hole that are created because the black hole’s powerful gravity drives binary stars to merge into one. In our galaxy, massive stars primarily come in pairs. The star suffered an abrasion to its outer layer but otherwise will be fine.

Keck Observatory

Credit and copyright: Ethan Tweedie Photography

The team utilized the Keck Observatory’s adaptive optics technology, a powerful technology that corrects the distorting effects of the Earth’s atmosphere in real time to more clearly reveal the space around the supermassive black hole.

Links: full UCLA press release, Keck press release.

An uncrewed Chinese lunar probe was launched on October 23, 2014, to fly around the Moon and back to Earth, in an 8-day mission. Called Chang’e 5-T1, it was a test mission in advance of the Chinese 2017 Chang’e 5 mission that is planned to return lunar rocks and soil to Earth. The return capsule of Chang’e 5-T1 landed in Inner Mongolia, on October 31, 2014.
Chang'e 5T1

Credit: CASC/CCTV

Like its predecessors, the spacecraft is named after the Chinese Moon goddess Chang’e.
Links: report on SpaceFlight101.com
Astronomy Picture of the Day (APOD) for November 1, 2014, shows Mars the day after Comet Siding Spring’s close encounter, with the comet visible at the edge of its overexposed disk.

Credit & copyright: Rolando Ligustri (CARA Project, CAST)

The caption describes: “this comet [came] within 86,700 miles or so of Mars, about one-third the Earth-Moon distance. Earth’s spacecraft and rovers in Mars orbit and on the surface reported no ill effects though, and had a ringside seat as a visitor from the outer Solar System passed by.”
A series of images (Fig. 13-12, p. 338) shows the eruption of V838 Monocerotis.
V838-Monocerotis

Credit: NASA, ESA and H.E. Bond (STScI)

The text says:
“An especially peculiar, and still poorly understood, eruption was V838 Monocerotis. This object brightened by a large amount, but probably for a different physical reason than normal novae. It was surrounded by many shells of dust that were “lit up” by the nova outburst. These “light echoes” evolved with time, as shells at different distances from the nova were successively illuminated. A consensus is emerging that its outbursts were from a violent merger of the two components of a binary star.”
Prof. Howard Bond of Penn State University writes (October 2014):
This consensus has been gaining even more popularity. The “Rosetta Stone” was the eruption of V1309 Scorpii in 2008…. It was in a field in the Galactic bulge that had been imaged by the OGLE project for about a decade before the outburst, and it turned out that the progenitor was a close binary, and it was even shown that its period was getting shorter up until the eruption.
A recent paper by Kochanek et al. estimates that a stellar merger occurs in the Milky Way about once every 5 years, so these are actually pretty common events.